Monte Kronio rises 1,300 feet above the geothermally active landscape of southwestern Sicily. Hidden in its bowels is a labyrinthine system of caves, filled with hot sulfuric vapors. At lower levels, these caves average 99 degrees Fahrenheit and 100 percent humidity. Human sweat cannot evaporate and heat stroke can result in less than 20 minutes of exposure to these underground conditions. Nonetheless, people have been visiting the caves of Monte Kronio since as far back as 8,000 years ago. They’ve left behind vessels from the Copper Age (early sixth to early third millennium B.C.) as well as various sizes of...